Aligned shingled writing for magnetic recording media and media having shingle edge positioned tracks

ABSTRACT

A method according to one embodiment includes gathering information about how an array of writers write and/or are expected to write to a magnetic medium during shingled recording, and computing, using the gathered information, data describing a lateral writing position to use during writing such that shingled track edges are aligned according to a format. A method according to another embodiment includes obtaining a lateral offset from a nominal writing position, and applying the lateral offset for repositioning a writing position of an array of writers relative to a nominal writing position during writing in a first direction. A product according to one embodiment includes a magnetic recording medium; and data indicative of whether a lateral writing position offset was used while writing.

BACKGROUND

The present invention relates to data storage systems, and moreparticularly, this invention relates to edge placement of written datato achieve aligned shingled writing.

In magnetic storage systems, magnetic transducers read data from andwrite data onto magnetic recording media. Data is written on themagnetic recording media by moving a magnetic recording transducer to aposition over the media where the data is to be stored. The magneticrecording transducer then generates a magnetic field, which encodes thedata into the magnetic media. Data is read from the media by similarlypositioning the magnetic read transducer and then sensing the magneticfield of the magnetic media. Read and write operations may beindependently synchronized with the movement of the media to ensure thatthe data can be read from and written to the desired location on themedia.

An important and continuing goal in the data storage industry is that ofincreasing the density of data stored on a medium. For tape storagesystems, that goal has led to increasing the track and linear bitdensity on recording tape, and decreasing the thickness of the magnetictape medium. However, the development of small footprint, higherperformance tape drive systems has created various problems in thedesign of a tape head assembly for use in such systems.

In a tape drive system, the drive moves the magnetic tape over thesurface of the tape head at high speed. Usually the tape head isdesigned to minimize the spacing between the head and the tape. Thespacing between the magnetic head and the magnetic tape is crucial andso goals in these systems are to have the recording gaps of thetransducers, which are the source of the magnetic recording flux in nearcontact with the tape to effect writing sharp transitions, and to havethe read elements in near contact with the tape to provide effectivecoupling of the magnetic field from the tape to the read elements.

The quantity of data stored on a magnetic tape may be expanded byincreasing the number of data tracks across the tape. Moreover, byoverlapping portions of data tracks (e.g., shingling data tracks),improvements to data storage quantities are achieved.

BRIEF SUMMARY

A method according to one embodiment includes gathering informationabout how an array of writers write and/or are expected to write to amagnetic medium during shingled recording, and computing, using thegathered information, data describing a lateral writing position to useduring writing such that shingled track edges are aligned according to aformat.

A method according to another embodiment includes obtaining a lateraloffset from a nominal writing position, and applying the lateral offsetfor repositioning a writing position of an array of writers relative toa nominal writing position during writing in a first direction.

A product according to one embodiment includes a magnetic recordingmedium; and data indicative of whether a lateral writing position offsetwas used while writing.

A computer program product according to one embodiment includes acomputer readable storage medium having program instructions embodiedtherewith, the program instructions executable by a controller to causethe controller to perform one or more of the foregoing methods.

Any of these embodiments may be implemented in a magnetic data storagesystem such as a tape drive system, which may include a magnetic head, adrive mechanism for passing a magnetic medium (e.g., recording tape)over the magnetic head, and a controller electrically coupled to themagnetic head.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a schematic diagram of a simplified tape drive systemaccording to one embodiment.

FIG. 1B is a schematic diagram of a tape cartridge according to oneembodiment.

FIG. 2 illustrates a side view of a flat-lapped, bi-directional,two-module magnetic tape head according to one embodiment.

FIG. 2A is a tape bearing surface view taken from Line 2A of FIG. 2.

FIG. 2B is a detailed view taken from Circle 2B of FIG. 2A.

FIG. 2C is a detailed view of a partial tape bearing surface of a pairof modules.

FIG. 3 is a partial tape bearing surface view of a magnetic head havinga write-read-write configuration.

FIG. 4 is a partial tape bearing surface view of a magnetic head havinga read-write-read configuration.

FIG. 5 is a side view of a magnetic tape head with three modulesaccording to one embodiment where the modules all generally lie alongabout parallel planes.

FIG. 6 is a side view of a magnetic tape head with three modules in atangent (angled) configuration.

FIG. 7 is a side view of a magnetic tape head with three modules in anoverwrap configuration.

FIGS. 8A-8F are partial representational views of shingled data tracksaccording to different embodiments.

FIG. 9 is a flowchart of a method according to one embodiment.

FIGS. 10A-10B are graphs of the bytes/C2 readback error rate vs. lateralread offset before and after applying a lateral write position offset.

FIG. 11 is a flowchart of a method according to one embodiment.

FIG. 12A is a diagram of a tape with shingled tracks written in anon-serpentine fashion according to one embodiment.

FIG. 12B is a diagram of a tape with shingled tracks written in aserpentine fashion according to one embodiment.

FIG. 12C is a diagram of a tape with shingled tracks written in aserpentine fashion and showing a directional buffer, according to oneembodiment.

FIG. 13 is a flowchart of a method according to one embodiment.

FIG. 14 is a representational diagram of a tape having shingled datatracks according to one embodiment.

FIG. 15A is a representational diagram of a shingled data trackaccording to one embodiment.

FIG. 15B is a graph illustrating readback errors v. reader offsetaccording to one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems, as well as operation and/or component partsthereof.

In one general embodiment, a method includes gathering information abouthow an array of writers write and/or are expected to write to a magneticmedium during shingled recording, and computing, using the gatheredinformation, data describing a lateral writing position to use duringwriting such that shingled track edges are aligned according to aformat.

In another general embodiment, a method includes obtaining a lateraloffset from a nominal writing position, and applying the lateral offsetfor repositioning a writing position of an array of writers relative toa nominal writing position during writing in a first direction.

In another general embodiment, a product includes a magnetic recordingmedium; and data indicative of whether a lateral writing position offsetwas used while writing.

In yet another general embodiment, a computer program product includes acomputer readable storage medium having program instructions embodiedtherewith, the program instructions executable by a controller to causethe controller to perform one or more of the foregoing methods.

FIG. 1A illustrates a simplified tape drive 100 of a tape-based datastorage system, which may be employed in the context of the presentinvention. While one specific implementation of a tape drive is shown inFIG. 1A, it should be noted that the embodiments described herein may beimplemented in the context of any type of tape drive system.

As shown, a tape supply cartridge 120 and a take-up reel 121 areprovided to support a tape 122. One or more of the reels may form partof a removable cartridge and are not necessarily part of the drive 100.The tape drive, such as that illustrated in FIG. 1A, may further includedrive motor(s) to drive the tape supply cartridge 120 and the take-upreel 121 to move the tape 122 over a tape head 126 of any type. Suchhead may include an array of readers, writers, or both.

Guides 125 guide the tape 122 across the tape head 126. Such tape head126 is in turn coupled to a controller 128 via a cable 130. Thecontroller 128, may be or include a processor and/or any logic forcontrolling any subsystem of the drive 100. For example, the controller128 typically controls head functions such as servo following, datawriting, data reading, etc. The controller 128 may include at least oneservo channel and at least one data channel, each of which include dataflow processing logic configured to process and/or store information tobe written to and/or read from the tape 122. The controller 128 mayoperate under logic known in the art, as well as any logic disclosedherein, and thus may be considered as a processor for any of thedescriptions of tape drives included herein, in various embodiments. Thecontroller 128 may be coupled to a memory 136 of any known type, whichmay store instructions executable by the controller 128. Moreover, thecontroller 128 may be configured and/or programmable to perform orcontrol some or all of the methodology presented herein. Thus, thecontroller 128 may be considered to be configured to perform variousoperations by way of logic programmed into one or more chips, modules,and/or blocks; software, firmware, and/or other instructions beingavailable to one or more processors; etc., and combinations thereof.

The cable 130 may include read/write circuits to transmit data to thehead 126 to be recorded on the tape 122 and to receive data read by thehead 126 from the tape 122. An actuator 132 controls position of thehead 126 relative to the tape 122.

An interface 134 may also be provided for communication between the tapedrive 100 and a host (internal or external) to send and receive the dataand for controlling the operation of the tape drive 100 andcommunicating the status of the tape drive 100 to the host, all as willbe understood by those of skill in the art.

FIG. 1B illustrates an exemplary tape cartridge 150 according to oneembodiment. Such tape cartridge 150 may be used with a system such asthat shown in FIG. 1A. As shown, the tape cartridge 150 includes ahousing 152, a tape 122 in the housing 152, and a nonvolatile memory 156coupled to the housing 152. In some approaches, the nonvolatile memory156 may be embedded inside the housing 152, as shown in FIG. 1B. In moreapproaches, the nonvolatile memory 156 may be attached to the inside oroutside of the housing 152 without modification of the housing 152. Forexample, the nonvolatile memory may be embedded in a self-adhesive label154. In one preferred embodiment, the nonvolatile memory 156 may be aFlash memory device, ROM device, etc., embedded into or coupled to theinside or outside of the tape cartridge 150. The nonvolatile memory isaccessible by the tape drive and the tape operating software (the driversoftware), and/or other device.

By way of example, FIG. 2 illustrates a side view of a flat-lapped,bi-directional, two-module magnetic tape head 200 which may beimplemented in the context of the present invention. As shown, the headincludes a pair of bases 202, each equipped with a module 204, and fixedat a small angle α with respect to each other. The bases may be“U-beams” that are adhesively coupled together. Each module 204 includesa substrate 204A and a closure 204B with a thin film portion, commonlyreferred to as a “gap” in which the readers and/or writers 206 areformed. In use, a tape 208 is moved over the modules 204 along a media(tape) bearing surface 209 in the manner shown for reading and writingdata on the tape 208 using the readers and writers. The wrap angle θ ofthe tape 208 at edges going onto and exiting the flat media supportsurfaces 209 are usually between about 0.1 degree and about 3 degrees.

The substrates 204A are typically constructed of a wear resistantmaterial, such as a ceramic. The closures 204B are made of the same orsimilar ceramic as the substrates 204A.

The readers and writers may be arranged in a piggyback or mergedconfiguration. An illustrative piggybacked configuration comprises a(magnetically inductive) writer transducer on top of (or below) a(magnetically shielded) reader transducer (e.g., a magnetoresistivereader, etc.), wherein the poles of the writer and the shields of thereader are generally separated. An illustrative merged configurationcomprises one reader shield in the same physical layer as one writerpole (hence, “merged”). The readers and writers may also be arranged inan interleaved configuration. Alternatively, each array of channels maybe readers or writers only. Any of these arrays may contain one or moreservo track readers for reading servo data on the medium.

FIG. 2A illustrates the tape bearing surface 209 of one of the modules204 taken from Line 2A of FIG. 2. A representative tape 208 is shown indashed lines. The module 204 is preferably long enough to be able tosupport the tape as the head steps between data bands.

In this example, the tape 208 includes 4 to 32 data bands, e.g., with 16data bands and 17 servo tracks 210, as shown in FIG. 2A on a one-halfinch wide tape 208. The data bands are defined between servo tracks 210.Each data band may include a number of data tracks, for example 1024data tracks (not shown). During read/write operations, the readersand/or writers 206 are positioned to specific track positions within oneof the data bands. Outer readers, sometimes called servo readers, readthe servo tracks 210. The servo signals are in turn used to keep thereaders and/or writers 206 aligned with a particular set of tracksduring the read/write operations.

FIG. 2B depicts a plurality of readers and/or writers 206 formed in agap 218 on the module 204 in Circle 2B of FIG. 2A. As shown, the arrayof readers and writers 206 includes, for example, 16 writers 214, 16readers 216 and two servo readers 212, though the number of elements mayvary. Illustrative embodiments include 8, 16, 32, 40, and 64 activereaders and/or writers 206 per array, and alternatively interleaveddesigns having odd numbers of reader or writers such as 17, 25, 33, etc.An illustrative embodiment includes 32 readers per array and/or 32writers per array, where the actual number of transducer elements couldbe greater, e.g., 33, 34, etc. This allows the tape to travel moreslowly, thereby reducing speed-induced tracking and mechanicaldifficulties and/or execute fewer “wraps” to fill or read the tape.While the readers and writers may be arranged in a piggybackconfiguration as shown in FIG. 2B, the readers 216 and writers 214 mayalso be arranged in an interleaved configuration. Alternatively, eacharray of readers and/or writers 206 may be readers or writers only, andthe arrays may contain one or more servo readers 212. As noted byconsidering FIGS. 2 and 2A-B together, each module 204 may include acomplementary set of readers and/or writers 206 for such things asbi-directional reading and writing, read-while-write capability,backward compatibility, etc.

FIG. 2C shows a partial tape bearing surface view of complementarymodules of a magnetic tape head 200 according to one embodiment. In thisembodiment, each module has a plurality of read/write (R/W) pairs in apiggyback configuration formed on a common substrate 204A and anoptional electrically insulative layer 236. The writers, exemplified bythe write transducer 214 and the readers, exemplified by the readtransducer 216, are aligned parallel to an intended direction of travelof a tape medium thereacross to form an R/W pair, exemplified by the R/Wpair 222. Note that the intended direction of tape travel is sometimesreferred to herein as the direction of tape travel, and such terms maybe used interchangeably. Such direction of tape travel may be inferredfrom the design of the system, e.g., by examining the guides; observingthe actual direction of tape travel relative to the reference point;etc. Moreover, in a system operable for bi-direction reading and/orwriting, the direction of tape travel in both directions is typicallyparallel and thus both directions may be considered equivalent to eachother.

Several R/W pairs 222 may be present, such as 8, 16, 32 pairs, etc. TheR/W pairs 222 as shown are linearly aligned in a direction generallyperpendicular to a direction of tape travel thereacross. However, thepairs may also be aligned diagonally, etc. Servo readers 212 arepositioned on the outside of the array of R/W pairs, the function ofwhich is well known.

Generally, the magnetic tape medium moves in either a forward or reversedirection as indicated by arrow 220. The magnetic tape medium and headassembly 200 operate in a transducing relationship in the mannerwell-known in the art. The piggybacked MR head assembly 200 includes twothin-film modules 224 and 226 of generally identical construction.

Modules 224 and 226 are joined together with a space present betweenclosures 204B thereof (partially shown) to form a single physical unitto provide read-while-write capability by activating the writer of theleading module and reader of the trailing module aligned with the writerof the leading module parallel to the direction of tape travel relativethereto. When a module 224, 226 of a piggyback head 200 is constructed,layers are formed in the gap 218 created above an electricallyconductive substrate 204A (partially shown), e.g., of AlTiC, ingenerally the following order for the R/W pairs 222: an insulating layer236, a first shield 232 typically of an iron alloy such as NiFe (−), CZTor Al—Fe—Si (Sendust), a sensor 234 for sensing a data track on amagnetic medium, a second shield 238 typically of a nickel-iron alloy(e.g., ˜80/20 at % NiFe, also known as permalloy), first and secondwriter pole tips 228, 230, and a coil (not shown). The sensor may be ofany known type, including those based on MR, GMR, AMR, tunnelingmagnetoresistance (TMR), etc.

The first and second writer poles 228, 230 may be fabricated from highmagnetic moment materials such as ˜45/55 NiFe. Note that these materialsare provided by way of example only, and other materials may be used.Additional layers such as insulation between the shields and/or poletips and an insulation layer surrounding the sensor may be present.Illustrative materials for the insulation include alumina and otheroxides, insulative polymers, etc.

The configuration of the tape head 126 according to one embodimentincludes multiple modules, preferably three or more. In awrite-read-write (W-R-W) head, outer modules for writing flank one ormore inner modules for reading. Referring to FIG. 3, depicting a W-R-Wconfiguration, the outer modules 252, 256 each include one or morearrays of writers 260. The inner module 254 of FIG. 3 includes one ormore arrays of readers 258 in a similar configuration. Variations of amulti-module head include a R-W-R head (FIG. 4), a R-R-W head, a W-W-Rhead, etc. In yet other variations, one or more of the modules may haveread/write pairs of transducers. Moreover, more than three modules maybe present. In further approaches, two outer modules may flank two ormore inner modules, e.g., in a W-R-R-W, a R-W-W-R arrangement, etc. Forsimplicity, a W-R-W head is used primarily herein to exemplifyembodiments of the present invention. One skilled in the art apprisedwith the teachings herein will appreciate how permutations of thepresent invention would apply to configurations other than a W-R-Wconfiguration.

FIG. 5 illustrates a magnetic head 126 according to one embodiment ofthe present invention that includes first, second and third modules 302,304, 306 each having a tape bearing surface 308, 310, 312 respectively,which may be flat, contoured, etc. Note that while the term “tapebearing surface” appears to imply that the surface facing the tape 315is in physical contact with the tape bearing surface, this is notnecessarily the case. Rather, only a portion of the tape may be incontact with the tape bearing surface, constantly or intermittently,with other portions of the tape riding (or “flying”) above the tapebearing surface on a layer of air, sometimes referred to as an “airbearing”. The first module 302 will be referred to as the “leading”module as it is the first module encountered by the tape in a threemodule design for tape moving in the indicated direction. The thirdmodule 306 will be referred to as the “trailing” module. The trailingmodule follows the middle module and is the last module seen by the tapein a three module design. The leading and trailing modules 302, 306 arereferred to collectively as outer modules. Also note that the outermodules 302, 306 will alternate as leading modules, depending on thedirection of travel of the tape 315.

In one embodiment, the tape bearing surfaces 308, 310, 312 of the first,second and third modules 302, 304, 306 lie on about parallel planes(which is meant to include parallel and nearly parallel planes, e.g.,between parallel and tangential as in FIG. 6), and the tape bearingsurface 310 of the second module 304 is above the tape bearing surfaces308, 312 of the first and third modules 302, 306. As described below,this has the effect of creating the desired wrap angle α₂ of the taperelative to the tape bearing surface 310 of the second module 304.

Where the tape bearing surfaces 308, 310, 312 lie along parallel ornearly parallel yet offset planes, intuitively, the tape should peel offof the tape bearing surface 308 of the leading module 302. However, thevacuum created by the skiving edge 318 of the leading module 302 hasbeen found by experimentation to be sufficient to keep the tape adheredto the tape bearing surface 308 of the leading module 302. The trailingedge 320 of the leading module 302 (the end from which the tape leavesthe leading module 302) is the approximate reference point which definesthe wrap angle α₂ over the tape bearing surface 310 of the second module304. The tape stays in close proximity to the tape bearing surface untilclose to the trailing edge 320 of the leading module 302. Accordingly,read and/or write elements 322 may be located near the trailing edges ofthe outer modules 302, 306. These embodiments are particularly adaptedfor write-read-write applications.

A benefit of this and other embodiments described herein is that,because the outer modules 302, 306 are fixed at a determined offset fromthe second module 304, the inner wrap angle α₂ is fixed when the modules302, 304, 306 are coupled together or are otherwise fixed into a head.The inner wrap angle α₂ is approximately tan⁻¹(δ/W) where δ is theheight difference between the planes of the tape bearing surfaces 308,310 and W is the width between the opposing ends of the tape bearingsurfaces 308, 310. An illustrative inner wrap angle α₂ is in a range ofabout 0.3° to about 1.1°, though can be any angle required by thedesign.

Beneficially, the inner wrap angle α₂ on the side of the module 304receiving the tape (leading edge) will be larger than the inner wrapangle α₃ on the trailing edge, as the tape 315 rides above the trailingmodule 306. This difference is generally beneficial as a smaller α₃tends to oppose what has heretofore been a steeper exiting effectivewrap angle.

Note that the tape bearing surfaces 308, 312 of the outer modules 302,306 are positioned to achieve a negative wrap angle at the trailing edge320 of the leading module 302. This is generally beneficial in helpingto reduce friction due to contact with the trailing edge 320, providedthat proper consideration is given to the location of the crowbar regionthat forms in the tape where it peels off the head. This negative wrapangle also reduces flutter and scrubbing damage to the elements on theleading module 302. Further, at the trailing module 306, the tape 315flies over the tape bearing surface 312 so there is virtually no wear onthe elements when tape is moving in this direction. Particularly, thetape 315 entrains air and so will not significantly ride on the tapebearing surface 312 of the third module 306 (some contact may occur).This is permissible, because the leading module 302 is writing while thetrailing module 306 is idle.

Writing and reading functions are performed by different modules at anygiven time. In one embodiment, the second module 304 includes aplurality of data and optional servo readers 331 and no writers. Thefirst and third modules 302, 306 include a plurality of writers 322 andno data readers, with the exception that the outer modules 302, 306 mayinclude optional servo readers. The servo readers may be used toposition the head during reading and/or writing operations. The servoreader(s) on each module are typically located towards the end of thearray of readers or writers.

By having only readers or side by side writers and servo readers in thegap between the substrate and closure, the gap length can besubstantially reduced. Typical heads have piggybacked readers andwriters, where the writer is formed above each reader. A typical gap is20-35 microns. However, irregularities on the tape may tend to droopinto the gap and create gap erosion. Thus, the smaller the gap is thebetter. The smaller gap enabled herein exhibits fewer wear relatedproblems.

In some embodiments, the second module 304 has a closure, while thefirst and third modules 302, 306 do not have a closure. Where there isno closure, preferably a hard coating is added to the module. Onepreferred coating is diamond-like carbon (DLC).

In the embodiment shown in FIG. 5, the first, second, and third modules302, 304, 306 each have a closure 332, 334, 336, which extends the tapebearing surface of the associated module, thereby effectivelypositioning the read/write elements away from the edge of the tapebearing surface. The closure 332 on the second module 304 can be aceramic closure of a type typically found on tape heads. The closures334, 336 of the first and third modules 302, 306, however, may beshorter than the closure 332 of the second module 304 as measuredparallel to a direction of tape travel over the respective module. Thisenables positioning the modules closer together. One way to produceshorter closures 334, 336 is to lap the standard ceramic closures of thesecond module 304 an additional amount. Another way is to plate ordeposit thin film closures above the elements during thin filmprocessing. For example, a thin film closure of a hard material such asSendust or nickel-iron alloy (e.g., 45/55) can be formed on the module.

With reduced-thickness ceramic or thin film closures 334, 336 or noclosures on the outer modules 302, 306, the write-to-read gap spacingcan be reduced to less than about 1 mm, e.g., about 0.75 mm, or 50% lessthan commonly-used LTO tape head spacing. The open space between themodules 302, 304, 306 can still be set to approximately 0.5 to 0.6 mm,which in some embodiments is ideal for stabilizing tape motion over thesecond module 304.

Depending on tape tension and stiffness, it may be desirable to anglethe tape bearing surfaces of the outer modules relative to the tapebearing surface of the second module. FIG. 6 illustrates an embodimentwhere the modules 302, 304, 306 are in a tangent or nearly tangent(angled) configuration. Particularly, the tape bearing surfaces of theouter modules 302, 306 are about parallel to the tape at the desiredwrap angle α₂ of the second module 304. In other words, the planes ofthe tape bearing surfaces 308, 312 of the outer modules 302, 306 areoriented at about the desired wrap angle α₂ of the tape 315 relative tothe second module 304. The tape will also pop off of the trailing module306 in this embodiment, thereby reducing wear on the elements in thetrailing module 306. These embodiments are particularly useful forwrite-read-write applications. Additional aspects of these embodimentsare similar to those given above.

Typically, the tape wrap angles may be set about midway between theembodiments shown in FIGS. 5 and 6.

FIG. 7 illustrates an embodiment where the modules 302, 304, 306 are inan overwrap configuration. Particularly, the tape bearing surfaces 308,312 of the outer modules 302, 306 are angled slightly more than the tape315 when set at the desired wrap angle α₂ relative to the second module304. In this embodiment, the tape does not pop off of the trailingmodule, allowing it to be used for writing or reading. Accordingly, theleading and middle modules can both perform reading and/or writingfunctions while the trailing module can read any just-written data.Thus, these embodiments are preferred for write-read-write,read-write-read, and write-write-read applications. In the latterembodiments, closures should be wider than the tape canopies forensuring read capability. The wider closures may require a widergap-to-gap separation. Therefore a preferred embodiment has awrite-read-write configuration, which may use shortened closures thatthus allow closer gap-to-gap separation.

Additional aspects of the embodiments shown in FIGS. 6 and 7 are similarto those given above.

A 32 channel version of a multi-module head 126 may use cables 350having leads on the same or smaller pitch as current 16 channelpiggyback LTO modules, or alternatively the connections on the modulemay be organ-keyboarded for a 50% reduction in cable span. Over-under,writing pair unshielded cables may be used for the writers, which mayhave integrated servo readers.

The outer wrap angles α₁ may be set in the drive, such as by guides ofany type known in the art, such as adjustable rollers, slides, etc. oralternatively by outriggers, which are integral to the head. Forexample, rollers having an offset axis may be used to set the wrapangles. The offset axis creates an orbital arc of rotation, allowingprecise alignment of the wrap angle α₁.

To assemble any of the embodiments described above, conventional u-beamassembly can be used. Accordingly, the mass of the resultant head may bemaintained or even reduced relative to heads of previous generations. Inother approaches, the modules may be constructed as a unitary body.Those skilled in the art, armed with the present teachings, willappreciate that other known methods of manufacturing such heads may beadapted for use in constructing such heads. Moreover, unless otherwisespecified, processes and materials of types known in the art may beadapted for use in various embodiments in conformance with the teachingsherein, as would become apparent to one skilled in the art upon readingthe present disclosure.

As previously mentioned, the quantity of data stored on a magnetic tapemay be expanded by overlapping portions of data tracks (e.g., shinglingdata tracks) and thereby increasing the number of data tracks across thetape. Shingling may be used to adjust written track width for writingnarrower tracks using wider legacy writers which enable so calledbackward compatibility. As a result, improvements to data storagequantities are achieved. However, these improvements to data storagequantities may come at the expense of readback performance inconventional products. Specifically, conventional products mayexperience a decline in readback performance resulting from a degree ofuncertainty with regard to the writer characteristics, and therefore,the characteristics of the tracks written by the writers. For example,the actual dimensions and/or position of one or more writers in a headmay be different than the nominal design dimensions and/or position ofthe one or more writers. This discrepancy between actual and nominaldesign characteristics of writers may result in a displacement of theedges of shingled tracks when written to media. The drive attempts toread back the shingled tracks in the nominal design reading position,but depending on the extent which shingled tracks are displaced from thenominal design position, the shingled tracks may cause increasedreadback errors and/or may not be readable at all.

FIGS. 8A-8C illustrate the difference which may exist between nominaldesign and actual characteristics (e.g., dimensions, positioning, etc.)of shingled tracks, respectively. FIG. 8A depicts the nominal designcharacteristics of shingled tracks to be written to tape based on thenominal design characteristics of the writers used to write the shingledtracks. Conceptually, this is what is what is expected to occur in use.As shown, the reader 802 is designed to be oriented at a positionanticipated to align with the written track 804 on tape as the tapemoves in the direction of tape travel relative to the reader 802. Thedashed line 803 depicts the expected edge of the shingled track 804,e.g., according to a format.

However, due to thin film wafer processing variations, the actualdimensions of the writer may be different than the designspecifications, even though the writer dimensions fall withintolerances. It follows that the positions of the edges of the shingledtracks may differ from the nominal design, thereby potentially resultingin causing reader misalignment with tracks and even spanning ontoadjacent tracks.

For example, as represented in FIGS. 8A and 8B, when the actual writerwidth is less than the nominal design writer width, the actual width WAof the physical track is narrower than the design width WD, which causesthe characteristics of the written tracks 804 on tape in FIG. 8B to bedifferent than the nominal design characteristics of the tracks, asdepicted in FIG. 8A. Particularly, though the centerlines 805 of thewritten (pre-shingled) tracks remains the same, and the width Ws of theshingled track is the same in FIGS. 8A and 8B, the upper edge of theshingled track 804 in FIG. 8B is offset (Offset) from the expectedlocation along line 803 in the cross-track direction 806 due to thenarrower actual writer width. The drive code positions the reader 802 inthe center of the nominal shingled track position as depicted in FIG.8A. Accordingly, a significant portion the reader 802 is outside of theshingled track 804 despite being oriented at a position anticipated toalign with nominal design characteristics of the written track 804.

As discussed in more detail below, various embodiments laterally correctthe writing position to minimize the misregistration, thereby enablingwriting of the readable portions of the shingled tracks in the nominaldesign position. Then, when a drive performs a readback operation, thereader is positioned properly above the shingled tracks. FIG. 8C depictsa shingled track 804 written with the corrected lateral writing positionapplied to minimize the reader misregistration.

As a result, it is desirable that the discrepancies between nominaldesign characteristics of shingled tracks and actual characteristics ofshingled tracks are mitigated. It should be noted that although theoffset is illustrated in FIGS. 8A-8C as being measured using an outsideedge of the data tracks, according to other approaches, an offset may bemeasured using a center point of the data tracks, or any other desiredreference point.

Similarly, FIGS. 8D-8F, having common numbering with FIGS. 8A-8C forsimilar components, depict the case where the actual writer width isgreater than the design width. FIG. 8D illustrates the design width WDof a (pre-shingled) track as written. FIG. 8E illustrates the effectthat occurs when the actual writer width is larger than the designwriter width, thereby causing the edge of the shingled track 804 to bedisplaced from the nominal design location along line 803. Variousembodiments correct the writing position to minimize the displacement,thereby enabling writing of shingled tracks in the intended positionspecified by the nominal design. Then, when a drive performs a readbackoperation, the reader is positioned properly above the shingled tracks.FIG. 8F depicts a shingled track 804 written with the corrected writingposition applied to minimize the reader misregistration.

The repositioning of readers was contemplated in order to reducereadback error rates, but was deemed impractical for removable mediawhich may have data appended by multiple drives, each having a differentshingled track placement error and thus requiring a different read headrepositioning requirement. Similarly, attempts to budget and therebycompensate for undesirable positioning of shingled tracks were found toresult in lower achievable areal density. Finally, reducing the readerwidth was deemed undesirable as resulting in lower readback amplitudebroadband signal to noise ratio.

Accordingly, various embodiments described herein enable accurate andoptimal implementations of shingled writing on magnetic media. Byconsidering the nominal design and actual characteristics of thewriters, accurate and predictable and optimal characteristics of theshingled tracks written to media may be achieved. Accordingly, a givenmedium may, in some embodiments, be accurately read in any one of aplurality of drives without making significant adjustments to the readhead position between drives, as will be described in further detailbelow.

Now referring to FIG. 9, a flowchart of a method 900 is shown accordingto one embodiment. The method 900 may be performed in any of theenvironments depicted in FIGS. 1-7, among others, in variousembodiments. Of course, more or less operations than those specificallydescribed in FIG. 9 may be included in method 900, as would beunderstood by one of skill in the art upon reading the presentdescriptions.

Each of the steps of the method 900 may be performed by any suitablecomponent of the operating environment. For example, in variousembodiments, the method 900 may be partially or entirely performed by acontroller (e.g., see 128 of FIG. 1A), a processor, etc., or some otherdevice having one or more processors therein. The processor, e.g.,processing circuit(s), chip(s), and/or module(s) implemented in hardwareand/or software, and preferably having at least one hardware componentmay be utilized in any device to perform one or more steps of the method900. Illustrative processors include, but are not limited to, a centralprocessing unit (CPU), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA), etc., combinationsthereof, or any other suitable computing device known in the art.

As shown in FIG. 9, method 900 includes operation 902, where informationabout how an array of writers actually write and/or are expected towrite to a magnetic medium during shingled recording is gathered. Again,differences between how writers are intended to write to a magneticmedium, and how writers actually write and/or are expected to write tothe magnetic medium result in degraded readback performance. Thus, bygathering information about how an array of writers actually writeand/or are expected to write to a magnetic medium as seen in operation902, such information may be used to improve the readback performance,e.g., by implementing a lateral writing position which is laterallyshifted from what would otherwise be a nominal actual writing positionto compensate for any discrepancies between actual and nominal designwriter characteristics, as will soon become apparent.

In some embodiments, the information gathered in operation 902 mayindicate that nominal design and actual characteristics of the writersare matched, e.g., a difference between the nominal design and actualcharacteristics of the writers is within a tolerance. Thus, in someembodiments an array of writers may write data tracks havingcharacteristics which sufficiently match nominal design characteristicsthereof. With continued reference to method 900, optional decision 904includes determining whether a difference between actual writerperformance and nominal design writer performance is acceptable, e.g.,within an acceptable range, less than some predefined value delineatingacceptable performance from unacceptable performance, etc. In responseto determining that the difference is acceptable, method 900 may end, orproceed to operation 902 such that information about how another arrayof writers is writing may be gathered, e.g., the writers on an opposingmodule. Accordingly, data may be written and efficiently read withoutimplementing a lateral writing position. It follows that in someapproaches, application of an offset to the nominal lateral writingposition may be disengaged by such determination, by user override,waived upon detecting a predetermined condition, etc.

However, upon determining that a difference between actual writerperformance and nominal design writer performance is not acceptable,method 900 proceeds to operation 906 which includes using the gatheredinformation to compute data describing an offset lateral writingposition to use during writing such that shingled track edges arealigned according to a format. For example, the data describing thelateral writing position may represent a lateral offset to apply to anominal writing position during writing operations, e.g., resulting inthe transitions of writing positions from FIGS. 8B to 8C and 8E to 8F.The lateral writing position may be based, at least in part, on alateral offset between nominal design and actual characteristics ofwriters and/or data tracks written by writers. In other words,implementing a computed lateral writing position during writingdesirably overcomes any discrepancies (e.g., lateral misregistrations)between the nominal design and actual characteristics of the writers. Asa result, in operation 908, data may be written to magnetic media (e.g.,tape) by using the data describing the lateral writing position, e.g.,by applying an offset to the nominal writing position. This solution mayenable different drives to accurately read the data, without having toattempt to compensate for shingled track edge offsets by repositioningthe reading position away from nominal, because the data is written inthe correct position from the outset.

In addition, according to some approaches, the lateral writing positionmay be further adjusted to compensate for additional trackcharacteristics, e.g., to avoid and/or compensate for curved edges ofthe magnetic transitions which form along the edges of the data tracks.According to an example, the lateral writing position may be laterallyrepositioned by about an additional 2-10% of the shingled track widthtowards the curved edges of the magnetic transitions of the track beingread, or vice versa. Thus, in some embodiments, the readable portion ofwritten tracks may be reduced by the extent of the curved portion. Inthis case, the “edge” of the shingled track may refer to the edge of theproperly written portion.

According to some embodiments, the data describing a lateral writingposition may be computed once for every drive, e.g., at a point ofmanufacture. For example, a drive carcass (e.g., having no head) mayreceive and be coupled to a given head, after which one or more of theprocesses described herein may be performed to determine an offsetlateral writing position to be implemented in future write operations.In other embodiments, the data describing a lateral writing position maybe computed in response to some criterion, such as in response to a higherror rate, upon receiving an instruction to perform the computation(e.g., on demand), upon a repair of the drive, after a predeterminedquantity of use of the drive, etc.

According to some embodiments, the information gathered in operation 902may be based on the physical construction of the writers themselves. Inone approach, the information gathered in operation 902 above may begathered by determining physical characteristics of magnetic poles ofthe writers in the array. The physical characteristics of magnetic polesmay include stripe height, thickness, cross-track width, pitch (e.g.,center-to-center) between writers of an array, etc., depending on thedesired embodiment. Moreover, physical characteristics of writers may bedetermined using an Atomic Force Microscope (AFM) or any other fineanalysis device which would be apparent to one skilled in the art, e.g.,to detect the location of edges of each pole.

As previously mentioned, characteristics of writers may vary as a resultof manufacturing imperfections, material properties, operator error,etc. For example, undesirable and/or unpredicted positioning of shingledtracks may result from a deviation of writing track width from a nominaldesign value. It follows that two writers may have noticeably differentphysical characteristics, although it may be intended that theirphysical characteristics are substantially the same. As a result, a datatrack written by one of the writers may be noticeably different from adata track written by the second writer (e.g., as seen above in FIGS. 8Band 8E). These differences are desirably accounted for by implementingthe operations of method 900.

Discrepancies between nominal design and actual characteristics ofwriters may result in a lateral displacement between nominal design andactual locations of data tracks when written to media, e.g., as seen inFIGS. 8A-8F. For example, a data track written to tape by an array ofwriters may have a lateral offset between a reference point at a nominaldesign position of the data track on the tape and a reference point atthe actual position of the data track on the tape. By determining thelateral offset corresponding to a given array of writers, datadescribing a lateral writing position to use during writing may becomputed such that shingled track edges are aligned according to aformat. Thus, implementing the computed lateral writing position whenwriting data to a magnetic medium may result in improved magnetic trackplacement and reduced readback error rates.

Moreover, as previously mentioned, the information about how an array ofwriters actually write and/or are expected to write data to a medium maybe gathered from various sources and/or using various processes.According to other embodiments, information about how an array ofwriters actually write and/or are expected to write to a magnetic mediumduring shingled recording may be gathered by evaluating the writingperformance of an array of writers in each drive. It should be notedthat the various embodiments described herein may be implemented inembodiments having multiple writers which may be capable of concurrentlywriting multiple tracks. Accordingly, there may be space between each ofthe multiple writers in a given embodiment thereby enabling shingledwriting to multiple tracks concurrently, as would be appreciated by oneskilled in the art upon reading the present description.

In one approach, the information about how an array of writers actuallywrite and/or are expected to write to a magnetic medium during shingledrecording may be gathered by imaging magnetic domains of data tracksafter they have been written by the array of writers to a magneticmedium. Thus, the data written by an array of writers may itself beexamined to determine information about how the array of writersactually write and/or are expected to write to a magnetic medium.Depending on the desired approach, imaging magnetic domains of writtendata tracks may be performed using a Magnetic Force Microscope (MFM),magnetic fluid developing, etc. By imaging magnetic domains of writtendata tracks, characteristics of the corresponding array of writers maybe derived therefrom and desirably used to compute data describing anoffset lateral writing position to use during writing (e.g., seeoperation 906 above), such as may be inferred in part by determining thewidths of the portions of the written tracks having straight (notcurved) transitions. Moreover, implementing the computed lateral writingposition when writing data to a magnetic medium results in improvedmagnetic track placement and reduced readback error rates.

According to an exemplary embodiment, an array of writers may be used towrite data to a magnetic tape while the head having the writers ispositioned at a nominal writing position in a drive. The nominal writingposition may be selected using any conventional approach. For example,the nominal writing position may be a predefined writing positionaccording to a format, a default writing position of the drive, acomputed position, etc., depending on the desired approach. Accordingly,the nominal writing position may correspond to nominal designcharacteristics of the writers (e.g., dimensions, positions, etc.).

Once data has been written to tracks by writers oriented in the nominalwriting position, a lateral offset separating the nominal design andactual locations of the data tracks may be determined by sweeping aposition of a head in the cross-track direction while attempting to readdata from the tracks. According to an exemplary approach, readers may bepositioned at an outermost position relative to corresponding datatracks, whereby the readers may begin reading or attempting to read datafrom the data tracks. After an occurrence, such as after an amount oftime has passed, a length of tape has been run, an amount of data hasbeen read, etc., the position of the readers may be repositioned. Theposition of the readers relative to the data tracks may be graduallyaltered by incrementally stepping the readers in the cross-trackdirection by some predefined distance, e.g., about 10 nm to about 100 nmper step for about ten or more datasets, away from the outermostposition. Thus, as the position of the readers is continuallyrepositioned, the readers are incrementally repositioned across thecross-track width of the data tracks to various lateral readingpositions relative to tracks having the written data.

The data read at the various lateral reading positions may be analyzedto determine the proper writing offset to apply during subsequentwriting. For example, upon evaluating the readback information gatheredby the readers as they are swept across the data tracks, a preferredlateral reading position for the readers may be determined. According toone approach, which is in no way intended to limit the invention, one ofthe lateral reading positions may be selected as a preferred lateralreading position based at least in part on an error rate experiencedduring the reading. For example, the lateral reading positioncorresponding to the lowest error rate experienced during reading of thedata tracks may be selected as the preferred lateral reading position.The error rate may be a C2 error rate, or may be any error rate metric,such as a C1 error rate, raw bit error rate, median bit error rate,average bit error rate, mean square error, etc. depending on the desiredembodiment as would be appreciated by one skilled in the art uponreading the present description. Moreover, the selected lateral readingposition may be used to compute data describing a lateral writingposition to implement during writing such that shingled track edges arealigned according to a format. For example, the offset of the selectedlateral reading position from a nominal position may be indicative ofthe offset of the shingled track edges, e.g., as in FIGS. 8B and 8E, andthus used to determine how to reposition the lateral writing position.It follows that information concerning the lateral offset for a givenarray of writers may be gathered from data written to a magneticrecording medium from a nominal writing position by reading the data atvarious laterally spaced reading positions relative to tracks having thedata written thereto.

According to some approaches, data may be read from the data tracksusing the same drive as the drive having the array of writers whichwrote the data tracks. Thus, the selected lateral reading position maycorrespond to the offset lateral writing position specifically for thedrive.

However, in other approaches data may be read from the data tracks usinga different drive than the drive having the array of writers which wrotethe data tracks. Specifically, data tracks corresponding to variousimplementations may be read using a common drive which is different thaneach of the drives having the array of writers which wrote the datatracks. The common drive may include a calibrated read head havingreader design tolerances. The data describing a lateral writing positionmay be computed based on readback signals from the common drive. Notethat the calculated data describing the lateral writing position isapplied to the drive that wrote the data tracks for correctingsubsequently written shingled tracks. Optionally, the common drive mayhave a head comprised of significantly narrower readers which mayimprove the precision in determining the optimum offset.

According to another exemplary embodiment, an array of writers may beused to write data to a magnetic tape while a position of the headhaving the writers is repositioned relative to the tape in a drive. Thearray of writers may be repositioned between various lateral writingpositions relative to the magnetic medium during the writing, therebycausing edges of the written tracks to reposition laterally with eachstep to a subsequent lateral writing position. According to an exemplaryapproach, writers may be positioned at an outermost position relative tocorresponding data tracks, whereby the writers may begin writing to thedata tracks. After an occurrence, such as an amount of time has passed,a length of tape has been run, an amount of data has been written, etc.,the position of the writers may be repositioned laterally. The positionof the writers relative to the data tracks may be gradually altered byincrementally stepping the writers in the cross-track direction by apredetermined distance, e.g., by about 10 nm to about 100 nm for aboutten or more datasets, away from the outermost position. Thus, as theposition of the writers continues to move laterally, the writersincrementally sweep across the cross-track width of the data trackswhile writing data thereto.

The data written to the tracks is read by readers oriented at apredefined, e.g., nominal, reading position. The nominal readingposition may be a predefined reading position according to a format, adefault reading position of the drive, a computed position, etc.Accordingly, the nominal reading position may correspond to nominaldesign characteristics of the writers (e.g., dimensions, positions,etc.).

As the readers pass over the laterally shifted shingled data tracks anddata is read therefrom, readback information may be gathered andevaluated. Moreover, upon evaluating the readback information, datadescribing a lateral writing position to use during subsequent writingbased on readback information acquired during the reading may becomputed. For example, a preferred offset lateral writing position maybe determined. According to one approach, which is in no way intended tolimit the invention, one of the lateral writing positions may beselected as a preferred lateral writing position based at least in parton an error rate experienced while reading data that was written whilethe writer was at that particular lateral position. For example, thelateral writing position corresponding to the lowest error rateexperienced while reading the data tracks may be selected as thepreferred lateral writing position. In another approach, an algorithmmay process the information read back from the track written atdiffering lateral locations and outputs the data describing the writingposition to use, potentially based on a median, bit error rate, C2 errorrate, mean square error rate, etc.

Thus, as opposed to writing in a specific location and sweeping thereaders thereacross to determine a preferred lateral read position, thewriters may be stepped across the tape in the cross-track directionwhile writing data to the tape such that readers may read the data froma set of nominal reading positions to determine a preferred lateralwriting position.

As described above, the data may be read by the same drive as the drivehaving the array of writers which wrote the data tracks, therebycorrelating the offset lateral writing position specifically with thegiven drive. However, in other approaches data may be read from the datatracks using a different drive than the drive having the array ofwriters which wrote the data tracks. The common drive may include acalibrated read head having small reader design tolerances. Thus, thecomputed data describing a lateral writing position may be based on bothreader and writer calibration data. Note that the calculated datadescribing the lateral writing position is applied to the drive thatwrote the data tracks for correcting subsequently written shingledtracks.

After an offset lateral writing position is determined using any of theprocesses described and/or suggested herein, the offset lateral writingposition is preferably applied during subsequent shingled writing. Asdescribed above, the offset lateral writing position may be used toreposition a writing position of the array of writers from a nominalwriting position to better mirror the actual characteristics of thewriters and/or readers of a given drive. By applying the offset lateralwriting position during subsequent shingled writing, improved magnetictrack placement and reduced readback error rates may desirably beachieved and improved interchange of tapes so written may be achieved.

Looking to FIG. 10A, graph 1000 depicts the bytes/C2 readback error ratevs. lateral read offset (lateral reading position) experienced whilereading a tape using conventional processes. Specifically, the resultsplotted in graph 1000 resulted from writing data tracks to and readingdata tracks from tape while relying on the nominal designcharacteristics of the writers and readers. However, as previouslydescribed, differences may exist between nominal design and actualcharacteristics of writers, thereby resulting in differences betweenintended and actual data tracks, e.g., as seen in FIGS. 8A-8F.Accordingly, a reader may be oriented at a position anticipated to alignwith a data track according to the nominal design characteristics of anarray of writers, yet, the actual characteristics of the written trackmay differ, thereby causing readers to be misaligned with the track andpossibly even span onto adjacent tracks.

Referring still to FIG. 10A, “0” along the x-axis of graph 1000represents the optimal reading position when reading tracks from a giventape according to the nominal design. However, the peaks of the plotsillustrated in graph 1000 represent the highest achieved bytes/C2readback error rate achieved by forcefully spanning readers laterallyfrom one side to the other side of the tracks in steps. Accordingly, thepeaks of the plots represent the actual optimal reading positiondetermined for the readers when reading from the tape. It follows thatassuming the nominal design characteristics of shingled tracks mirrorthe actual characteristics of shingled tracks produces inaccurateresults for both forward and reverse tape travel directions.

In sharp contrast, graph 1050 of FIG. 10B illustrates the resultsachieved after implementing an offset lateral writing position achievedusing an approach described herein. Similar results can be expectedusing any approach herein. As illustrated in graph 1050, “0” along thex-axis (the optimal reading position according to the nominal design)significantly aligns with the peaks of the plots (the actual optimalreading position) for both forward and reverse tape travel directions.Accordingly, by implementing an optimal lateral writing position toaccount for any differences between the nominal design and actualcharacteristics of the writers, improved readback performance isdesirably achieved.

However, as previously mentioned, it is in no way required to implementan offset lateral writing position while writing to magnetic media. Insome embodiments, the nominal design and actual characteristics of thewriters may be matched, a difference between the nominal design andactual characteristics of the writers may be within a design tolerance,etc. Thus, in some embodiments an array of writers may write data trackshaving characteristics which match nominal design characteristicsthereof. Accordingly, data may be written and efficiently read withoutimplementing an offset lateral writing position. It follows that in someapproaches, application of an offset lateral writing position may bedisengaged by user override, waived upon detecting a predeterminedcondition, etc. (e.g., see decision 904 above).

Referring now to FIG. 11, a flowchart of a method 1100 is shownaccording to an illustrative embodiment. The method 1100 may beperformed in accordance with the present invention in any of theenvironments depicted in FIGS. 1-7, among others, in variousembodiments. Of course, more or less operations than those specificallydescribed in FIG. 11 may be included in method 1100, as would beunderstood by one of skill in the art upon reading the presentdescriptions.

Each of the steps of the method 1100 may be performed by any suitablecomponent of the operating environment. For example, in variousembodiments, the method 1100 may be partially or entirely performed by acontroller (e.g., see 128 of FIG. 1A), a processor, etc., or some otherdevice having one or more processors therein. The processor, e.g.,processing circuit(s), chip(s), and/or module(s) implemented in hardwareand/or software, and preferably having at least one hardware componentmay be utilized in any device to perform one or more steps of the method1100. Illustrative processors include, but are not limited to, a CPU, anASIC, a FPGA, etc., combinations thereof, or any other suitablecomputing device known in the art.

As shown in FIG. 11, method 1100 includes operation 1102 in which alateral offset from a nominal writing position is obtained for a firstwriting direction. According to some embodiments, the lateral offset maybe obtained using any one or more of the operations described above withreference to method 900 of FIG. 9.

Referring still to method 1100, operation 1104 includes applying thelateral offset for repositioning a writing position of an array ofwriters from nominal writing positions during writing in a firstdirection. As described above, the lateral offset may be used todetermine an offset lateral writing position which repositions thewriting position of the array of writers away from a nominal writingposition to better mirror the actual characteristics of the writersand/or readers of a given drive. By applying the offset lateral writingposition offset during subsequent shingled writing, improved magnetictrack placement and reduced readback error rates may desirably beachieved.

Embodiments which implement bi-directional writing may include obtaininga second lateral offset to be applied when writing in a second directionopposite the first. Accordingly, method 1100 further includes optionaloperation 1106 where a second lateral offset is obtained for writing ina second direction opposite the first direction. Moreover, optionaloperation 1108 includes applying the second lateral offset duringwriting in the second direction, the second lateral offset beingdifferent than the lateral offset obtained in operation 1102.

Bi-directional shingled writing may be performed using serpentine ornon-serpentine writing. Moreover, depending on the configuration of thetransducers in a given module, more than one method of writing shingleddata tracks may be possible. For example, modules having areader-writer-reader (RWR) transducer configuration in a magnetic headmay conduct non-serpentine writing. This is primarily because a RWRtransducer configuration allows the same writer array to write eachadjoining data track, despite reversal of the tape direction and/ororientation of the transducer while writing thereto, as is achieved inserpentine writing in general. This may reduce writing errors, readbackerrors, data loss, etc., as well as reducing the misregistrationbudgeting requirements, as only one set of track tolerances comes intoplay. Moreover, using the same writer array to write adjoining datatracks ensures consistency while writing, e.g., by enabling accuratelateral offsets, lateral writing positions, symmetrical servo patternreading, overall higher areal density, etc.

Although the same writer array may be used to write adjoining datatracks in both first and second directions, different offset lateralwriting positions may be applied to the writer array for each of thedirections. As mentioned above in method 1100, a first lateral offsetmay be obtained and/or applied to reposition the writing position of anarray of writers from a nominal writing position to an offset lateralwriting position during writing in a first direction, while a secondlateral offset may be obtained and/or applied to reposition the writingposition of an array of writers from a nominal writing position to adifferent offset lateral writing position during writing in a seconddirection opposite the first direction, such as would be desired whenusing a single write head for serpentine writing in which the oppositewriting edges are used for the opposite directions.

Furthermore, it should be noted that in some embodiments, a lateraloffset may be predetermined (e.g., at a point of writing of the tape bya particular drive) and stored in memory. Thus, according to someapproaches, the lateral offset may be obtained from a media item such asa cartridge memory, from data encoded on the magnetic medium itself,etc., as described in further detail below. However, in other approachesthe lateral offset may also and/or alternatively be obtained from amemory of an apparatus performing the method, e.g., tape drive memory.In further approaches, the offset may be obtained from a database, froma host, from a library controller, etc.

In one embodiment, during operation, an indication indicating that thelateral offset was used while writing may be appended to a data set onthe medium. Equivalently, metadata describing that certain tracks werewritten using the writing offset may be stored to a memory such as thecartridge memory.

Looking now to FIGS. 12A-12C, representational diagrams of shingledwriting according to different embodiments are illustrated. A shingledtrack 1204 may be formed on a tape 1202 by writing a track 1206 over aportion of previously written track, thereby defining a shingled track1204 as a remaining portion of the previously written track. Indifferent embodiments, shingled tracks 1204 may be formed usingserpentine or non-serpentine writing as will soon become apparent.

As illustrated in the representational diagram of FIG. 12A, which is inno way intended to limit the invention, the orientation of the arrows ineach of the tracks are intended to represent the direction of tapetravel when the corresponding track was written to the tape 1202,preferably by a single array of writers configured for writing in bothwriting directions. Thus, a first offset lateral writing position may beapplied to the writer array while writing data to tracks in a firstdirection and a second offset lateral writing position may be applied tothe writer array while writing data to tracks in a second directionopposite the first direction, but this may not be necessary whenshingling as shown with the a given write head.

Note that, while not ideal, a writer-reader-writer (WRW) transducerconfiguration in a magnetic head may be used for non-serpentine writingin some embodiments. In such embodiments, it is preferable that, whilewriting data to adjoining data tracks, especially shingled data tracks,the same writer array is used for the adjoining data tracks. Moreover,similar to the description presented above, different writer arrays maynot be perfectly identical due to manufacturing variations, and thus mayhave different alignment characteristics, and therefore write datadifferently than may be intended. For example, the write transducers ofone writer array may not have the same pitch, spacing, etc. as the writetransducers of another writer array although uniformity may have beenintended. Thus, using multiple writer arrays to write data to adjoiningdata tracks may result in small track placement errors, as the datawritten to the tracks may be aligned differently on each pass. Accordingto another example, using different writer arrays may result inoverwriting data on an adjoining track, thereby causing data loss ifproper budgeting for this tolerance is not conducted.

However, according to another illustrative embodiment, a module may havea WRW transducer configuration, which is a preferable configuration withwhich to conduct serpentine writing. While writing data with a WRWconfiguration, the leading writer and reader are preferably active,while the trailing writer is not active, depending on the intendeddirection of tape travel. As a result, the leading writer array may beused to write adjoining data tracks for a first direction of tapetravel, while the trailing writer array may be used to write adjoiningdata tracks for a second direction of tape travel opposite the firstdirection. Again, a first lateral offset may be obtained and/or appliedto reposition the writing position of an array of writers from a nominalwriting position to an offset lateral writing position during writing ina first direction, while a second lateral offset may be obtained and/orapplied to reposition the writing locations of an array of writers froma nominal writing position to a different offset lateral writingposition during writing in a second direction opposite the firstdirection.

Looking now to the representational diagram of FIG. 12B, which is in noway intended to limit the invention, the orientation of the arrows ineach of the tracks are intended to represent the direction of tapetravel when the corresponding track was written to the tape 1202. Incontrast to the diagram of FIG. 12A, here data tracks corresponding to afirst direction of tape travel are written to the top portion of a datapartition, while data tracks corresponding to a second direction of tapetravel are written to the bottom portion of the data partition. Thispreferably reduces writing errors, readback errors, data loss, etc. andensures consistency while writing, e.g., by enabling symmetrical servopattern reading.

Furthermore, FIG. 12C depicts another serpentine writing pattern. Abuffer 1210, sometimes called a directional buffer, provides a spacingbetween the closest tracks written in opposite directions. In oneapproach, the amount of lateral repositioning may be reduced slightlyfrom the ideal amount to ensure that subsequent writing errors are notencountered, for example so that the directional buffer is maintainedsufficiently.

First tracks written adjacent to the directional buffer and tracksoverwritten by the last writing operation when a data band is completelyfilled desirably have a same tracking tolerance margin as all othershingled tracks.

In one approach, the algorithms used to select the optimum writingpositions account for the directional buffer, and ensure that therepositioned writing position does not adversely affect the directionalbuffer, e.g., by overwriting the directional buffer and perhaps into adata track on an opposite side of the directional buffer.

In an embodiment where tracks are written in opposite directions inserpentine fashion from outside in, the format may specify that the lasttrack written in a data band shingles the last track written in theopposite direction to maximize used area. The algorithm used to selectthe optimum writing positions may account for this and ensure that anyrepositioned writing position will not create an error such as byoverwriting a portion of the last track written in the oppositedirection.

It follows that various embodiments described herein may be implementedwith a product which includes a magnetic recording medium and datadescribing an offset lateral writing position to use during writing suchthat shingled track edges are aligned according to a format. Asdescribed above, the data describing the lateral writing position may beindicative of a lateral offset from the nominal writing position. Inother words, the data describing the lateral writing position mayrepresent an amount of space an array of writers should be offset from anominal writing position when writing data to the tape in order to matchthe actual and nominal design positioning of the data tracks.

According to an illustrative approach, the data describing the lateralwriting position may include information usable by a drive (e.g., see100 of FIG. 1A) having an algorithm that computes the lateral writingposition(s). The data may include values that are input into analgorithm to determine where and/or how to position a head having anarray of writers preferably such that the shingled track edges arealigned according to the format.

Moreover, according to some approaches, the data may be stored in amemory coupled to the magnetic recording medium. However, according toother approaches, the data may be encoded on the magnetic recordingmedium itself. For example, the data may be written to a designated areaof a tape.

Furthermore, some products having data written thereto may indicatewhether a lateral writing position offset was used while writing thedata. For example, a tape having shingled data tracks written by anarray of writers while offset at a lateral writing position may includean indication that the shingled tracks written thereto are aligned as aresult of implementing the offset lateral writing position. Theindication may be stored in a cartridge memory, written to a designatedarea of the tape (e.g., a header), stored in a tracking table (e.g., alookup table) not on the medium or cartridge e.g., in a librarycontroller, etc. Moreover, indications may be made which denote whethercertain wraps of a given tape were written using one or more offsetlateral writing position. Thus, an indication may include informationusable, e.g., by a drive, to determine how to read back data from themagnetic recording medium and/or perform further shingled writing. Forexample, a drive may implement lateral reader offsets (e.g., trackfollowing) while reading data from a tape written without using anoffset lateral writing position, yet while reading data from anothertape written using an offset lateral writing position, the drive mayread data therefrom using a nominal reading position. As a result,drives, accessors, controllers, etc. may be able to distinguish betweenthose tapes stored in a library and/or wraps thereof having alignedshingled tracks and those tapes stored in the library and/or wrapsthereof that may have misaligned shingled tracks.

It follows that a tape written using any of the processes describedand/or suggested herein is highly interchangeable and may effectively beused with any drive in view of the improved track alignment. This isbecause the track edges, having been corrected according to approachesherein, more closely approximate the nominal design track edge positionswhich the various drives may expect as a default, e.g., according to astandard.

Moreover, embodiments implementing an offset lateral writing positionmay be distinguished by comparing the characteristics of the actualwriters on the head with the characteristics of the data tracks writtenusing the writers. Upon determining that the characteristics of theactual writers on the head are offset from (e.g., do not match) thecharacteristics of the data tracks written using the writers, it may bedetermined that a lateral writing position has been employed to writethe data to the data tracks.

Exemplary Embodiment

FIG. 13 includes a flowchart which illustrates a method 1300 accordingto an in-use embodiment. The method 1300 may be performed in accordancewith the present invention in any of the environments depicted and/ordescribed herein. Of course, more or less operations than thosespecifically described in FIG. 13 may be included in method 1300, aswould be understood by one of skill in the art upon reading the presentdescriptions.

Each of the steps of the method 1300 may be performed by any suitablecomponent of the operating environment. For example, in variousembodiments, the method 1300 may be partially or entirely performed by acontroller (e.g., see 128 of FIG. 1A), a processor, etc., or some otherdevice having one or more processors therein. The processor, e.g.,processing circuit(s), chip(s), and/or module(s) implemented in hardwareand/or software, and preferably having at least one hardware componentmay be utilized in any device to perform one or more steps of the method1300. Illustrative processors include, but are not limited to, a CPU, anASIC, a FPGA, etc., combinations thereof, or any other suitablecomputing device known in the art.

Looking to FIG. 13, method 1300 includes writing a shingled track, e.g.,using a magnetic head having writer transducers coupled thereto. Seeoperation 1302. In order to write a shingled track, all write offsetsassociated with the head are preferably cleared. By clearing any writeoffsets associated with the head, the shingled track may be written suchthat any writer misalignments may be determined, as will soon becomeapparent.

Moreover, a shingled track is preferably formed by writing threeoverlapped tracks. Referring momentarily to FIG. 14, tape 1400 depicts afirst written track WT1, second written track WT2 and third writtentrack WT3. As shown, the tracks WT1 and WT2 are shingled (e.g.,partially overwritten) such that WT2 is sandwiched between WT1 and WT3,thereby defining the outer extents (track edges) of the shingled trackWT2. It is preferred that the second written track WT2 is written usingknown data while the first and third written tracks WT1, WT3 are writtendifferently than WT2. This allows a drive to determine when it is nearor at the track edges of WT2 when reading data written to WT2.

According to a preferred approach, WT2 may include formatted data fromany source, e.g., such as user data, as would be appreciated by oneskilled in the art upon reading the present description. For example,the formatted data may include data that has been deserialized tomultiple channels, encoded with error correction information, timeinterleaved, and/or compressed. In contrast, the first and/or thirdwritten tracks WT1, WT3 may include erased data, tone data, etc., or anyother pattern of data which is of a different type than the data writtento WT2. However, it should be noted that in some approaches, which arein no way intended to limit the invention, WT2 may have the same and/orsimilar data written thereto as written to WT1 and/or WT3 but offsetlinearly to allow distinguishing of the track edges of WT2.

Referring again to FIG. 13, operation 1304 includes measuring the readoffset, e.g., when reading a shingled track such as WT2. The read offsetmay be measured by selectively positioning a reader over a shingled datatrack and attempting to read data from the track. Specifically, a readermay be positioned at an outermost lateral position relative to theshingled track, and begin reading, or attempting to read, data from theshingled track. The outermost lateral position is preferably above orbeyond one of the track edges of the shingled track to be read. After anoccurrence, e.g., an amount of time has passed, a length of tape hasbeen run, an amount of data has been read, etc., the reader may berepositioned. The position of the reader relative to the data tracks maybe gradually altered by incrementally stepping the reader in thecross-track direction by some predetermined amount, e.g., about 10 nm toabout 100 nm for about ten or more datasets, away from the outermostposition. Thus, as the position of the reader is continuallyrepositioned, the reader incrementally sweeps across the cross-trackwidth of the data tracks to cover various lateral reading positionsrelative to shingled track having the written data.

Looking to FIG. 15A, a reader 1502 is shown at about an outermostposition relative to the shingled track 1504. Over time, the reader 1502may be continuously or incrementally swept across the track 1504 in thecross-track direction 1506, e.g., until reaching an opposite outermostposition relative to the shingled track 1504 (shown in shadow). Itfollows that as the position of the reader 1502 relative to the track1504 changes, the readback performance will change as well while data isread from the track 1504 as the track 1504 travels in the intendeddirection of tape motion 1508.

FIG. 15B includes a graph 1550 which outlines an exemplary readbackperformance that may be calculated as the reader 1502 is swept acrossthe shingled data track 1504. As shown, the readback performance isleast favorable as having the highest number of read errors occurringwhen the reader 1502 is positioned at about an outermost positionrelative to the shingled track 1504. However, as the reader 1502 movestowards the center of the shingled data track 1504, the number of readerrors experienced by the reader 1502 drops until a minimum value isachieved before rising again. The orientation of the reader 1502relative to the data track 1504 associated with the minimum valueprojected on the graph 1550 corresponds to an optimal reader position asdenoted. Moreover, the difference between the optimal reader positionand the position associated with zero offset (i.e., the origin on graph1550) indicates the optimal read offset.

Referring once again to FIG. 13, once the read offset has been measured,it may be used to determine a write offset which may be applied to amagnetic head having writer transducers coupled thereto. See operation1306.

In one approach, the data from a single reader may be used to determinethe writing position offset. In another approach, the data from multiplereaders may be used to determine the writing position offset, e.g., byusing an average, median, worst case, etc. of the relevant values. Usingdata from multiple readers may result in a more optimal selection of thecompensated writing position by averaging over the physical writervariations within the array. In one exemplary embodiment, the readbackdata within a predetermined interval of the median may be included inthe computation of the compensated writing position offset.

Optional operation 1308 includes writing another shingled track usingthe magnetic head having the write offset applied to its writingposition. As described above, a shingled track may be formed by writingthree overlapped tracks, e.g., see FIG. 14.

Furthermore, operation 1310 includes verifying that the read offset isnow approximately zero, e.g., in a manner similar to that measured inoperation 1304. For example, verifying the read offset may be performedby positioning a reader to about an outermost position relative to theshingled track having the write offset applied thereto, and moved acrossthe shingled track in the cross-track direction, e.g., see FIG. 15A and15B above. Thus, the verification of operation 1310 may includedetermining that the updated optimal read offset is at, or close to,zero.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

Moreover, a system according to various embodiments may include aprocessor and logic integrated with and/or executable by the processor,the logic being configured to perform one or more of the process stepsrecited herein. By integrated with, what is meant is that the processorhas logic embedded therewith as hardware logic, such as an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA), etc. By executable by the processor, what is meant is that thelogic is hardware logic; software logic such as firmware, part of anoperating system, part of an application program; etc., or somecombination of hardware and software logic that is accessible by theprocessor and configured to cause the processor to perform somefunctionality upon execution by the processor. Software logic may bestored on local and/or remote memory of any memory type, as known in theart. Any processor known in the art may be used, such as a softwareprocessor module and/or a hardware processor such as an ASIC, a FPGA, acentral processing unit (CPU), an integrated circuit (IC), etc.

It will be clear that the various features of the foregoing systemsand/or methodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

It will be further appreciated that embodiments of the present inventionmay be provided in the form of a service deployed on behalf of acustomer.

The inventive concepts disclosed herein have been presented by way ofexample to illustrate the myriad features thereof in a plurality ofillustrative scenarios, embodiments, and/or implementations. It shouldbe appreciated that the concepts generally disclosed are to beconsidered as modular, and may be implemented in any combination,permutation, or synthesis thereof. In addition, any modification,alteration, or equivalent of the presently disclosed features,functions, and concepts that would be appreciated by a person havingordinary skill in the art upon reading the instant descriptions shouldalso be considered within the scope of this disclosure.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A method, comprising: gathering information abouthow an array of writers write and/or are expected to write to a magneticmedium during shingled recording; and computing, using the gatheredinformation, data describing a lateral writing position to use duringwriting such that shingled track edges are aligned according to aformat.
 2. The method as recited in claim 1, wherein the informationabout how an array of writers write at nominal writing positions isgathered, wherein the data includes a lateral offset from the nominalwriting position.
 3. The method as recited in claim 1, wherein theinformation is gathered by writing data to a magnetic recording mediumusing writers of the array, reading data at various lateral readingpositions relative to tracks having the written data, and analyzing thedata read at the various lateral reading positions.
 4. The method asrecited in claim 3, wherein the data is read by a drive, the drive alsohaving the array of writers.
 5. The method as recited in claim 3,wherein the data is read by a different drive than a drive having thearray of writers.
 6. The method as recited in claim 5, wherein thedifferent drive is a calibrated drive.
 7. The method as recited in claim1, wherein the information is gathered by writing data to a magneticrecording medium using writers of the array, repositioning the arraybetween various lateral writing positions relative to the magneticmedium during the writing, reading data at a predefined readingposition, and computing data describing a lateral writing position touse during subsequent writing based on readback information acquiredduring the reading.
 8. The method as recited in claim 7, wherein thedata is read by a drive, the drive also having the array of writers. 9.The method as recited in claim 7, wherein the data is read by adifferent drive than a drive having the array of writers.
 10. The methodas recited in claim 1, wherein the information is gathered by imagingmagnetic domains of data tracks written by the array of writers.
 11. Themethod as recited in claim 1, wherein the information is gathered bydetermining physical characteristics of magnetic poles of the writers inthe array.
 12. The method as recited in claim 1, comprising applying thedata describing the lateral writing position during subsequent shingledwriting.
 13. An apparatus, comprising: a drive mechanism for passing amagnetic medium over the array of writers; a controller electricallycoupled to the array of writers; and logic integrated with and/orexecutable by the controller to perform the method of claim
 1. 14. Theapparatus as recited in claim 13, comprising logic configured to applythe lateral writing position for repositioning a writing position of thearray of writers from a nominal writing position.
 15. A method,comprising: obtaining a lateral offset from a nominal writing position;and applying the lateral offset for repositioning a writing position ofan array of writers relative to a nominal writing position duringwriting in a first direction.
 16. The method as recited in claim 15,wherein the lateral offset is obtained from a memory of an apparatusperforming the method.
 17. The method as recited in claim 15, comprisingobtaining a second lateral offset for writing in a second directionopposite the first direction; and applying the second lateral offsetduring writing in the second direction, the second lateral offset beingdifferent than the lateral offset.
 18. The method as recited in claim15, comprising appending an indication indicating that the lateraloffset was used while writing.
 19. An apparatus, comprising: a drivemechanism for passing a magnetic medium over the array of writers; acontroller electrically coupled to the array of writers; and logicintegrated with and/or executable by the controller to perform themethod of claim
 15. 20. A product, comprising: a magnetic recordingmedium; and data indicative of whether a lateral writing position offsetwas used while writing.
 21. The product as recited in claim 20, whereinthe data is stored in a memory coupled to the magnetic recording medium.22. The product as recited in claim 20, wherein the data is encoded onthe magnetic recording medium.
 23. The product as recited in claim 20,wherein data includes information usable by a drive to determine how toread back data from the magnetic recording medium.
 24. The product asrecited in claim 20, wherein the data indicative of whether a lateralwriting position offset was used while writing includes anidentification of which tracks were written using the lateral writingposition offset.
 25. A computer program product, the computer programproduct comprising a computer readable storage medium having programinstructions embodied therewith, the program instructions executable bya controller to cause the controller to perform a method comprising:gathering, by the controller, information about how an array of writerswrite and/or are expected to write to a magnetic medium during shingledrecording; and computing, by the controller using the gatheredinformation, data describing a lateral writing position to use duringwriting such that shingled track edges are aligned according to aformat.